#include <iostream>
#include <algorithm>
#include <iomanip>
#define MAXN 10005
#define INF 20
using namespace std;
int N, K;
double w[MAXN], v[MAXN], mix[MAXN];
void solve();
int main() {
    cin >> N >> K;
    for (int i = 0; i < N; i++) cin >> w[i] >> v[i];
    solve();
    return 0;
}

bool C(double x) {
    for (int i = 0; i < N; i++) mix[i] = -v[i] + w[i] * x;
    sort(mix, mix + N);
    double res = 0;
    for (int i = 0; i < K; i++) res += mix[i];
    return res <= 0;
}

void solve() {
    // [)
    double lower = 0, upper = INF;
    for (int i = 0; i < 100; i++) {
        double middle = (lower + upper) / 2;
        if (C(middle)) lower = middle;
        else upper = middle; 
    }

    cout << fixed << setprecision(2) << lower << endl;
}
